Silverfish

Silverfish are small hostile arthropods found infesting stone and deepslate blocks in mountain caves and certain structures, such as strongholds, or spawned using potions of Infestation. They attack by biting, and attacking one can cause nearby silverfish to break out of their blocks to attack the aggressor.

Silverfish spawn from broken infested blocks, which generate in strongholds, underground in mountains and windswept hills biomes, in igloo basements, and in woodland mansion false portal rooms. Silverfish do not appear if the block is broken with the Silk Touch enchantment.[1]

Silverfish monster spawners naturally generate in end portal rooms in strongholds. Silverfish can spawn from spawners at light level 11 or lower. In Java Edition, they can also spawn on stone types they can enter (stone, cobblestone, stone bricks, etc.) at any light level, and cannot spawn within a 5 block distance of any player[verify].